1. Field of the Invention and Contract Statement
This invention relates to a process for preparing gel spheres of nuclear fuel and to apparatus for conducting such process.
2. Division of Background and Prior Art
A sol gel process for the production of (U, Pu)O.sub.2 nuclear fuel microspheres is disclosed in U.S. Pat. No. 4,397,778. Because of the higher gelation temperature (about 85.degree. C.) required in such process, silicone oil is used as a gelation medium instead of trichloroethylene (TCE) which is used in conventional internal gelation processes for the preparation of UO.sub.3 spheres. The use of silicone oil, which has higher viscosity and higher surface tension, has caused some difficulties particularly in a continuous mode of operation of the process. Recently, improvements to the process have been disclosed that overcome such difficulties. One of the improvements is a method by which the resistance of the surface tension and viscosity of the silicone oil are overcome by transporting the liquid droplets of a sol or broth into the silicone oil gelation medium by way of a jet stream of silicone oil. Another improvement uses a draft tube and vibrated screen for disengaging the gelled and aged spheres from silicone oil and then transporting the disengaged spheres into a trichloroethylene wash column where the silicone oil is washed from the outer surfaces of such spheres. The application of such improvements to the process has resulted in a continuous internal gelation process for producing nuclear fuel microspheres of predictable size and quality. However, the process is now more complex and more difficult to control and maintain, especially since remote operation is required. It is desirable to have a more simplified process with fewer steps, fewer equipment pieces to control, and one that is more amenable to scale-up and remote operation and maintenance.
U.S. Pat. No. 4,124,535 discloses a method of forming gelled spheres by suspending droplets of a slurry in a suspending liquid, such as, perchloroethylene. The slurry includes slurries made from metal oxides, but radioactive materials are not mentioned.
U.S. Pat. No. 3,321,560 discloses a method of making uranium dioxide spheres by suspension of a uranium dioxide slurry in trichloroethylene. There is no disclosure of dropping uranium spheres into a moving stream of hot solvent.
U.S. Pat. No. 2,820,984 teaches the production of regenerated cellulose pellets. As the drops or globules of regenerated cellulose are formed, they are first dropped into a coagulating bath wherein they are subjected to a preliminary limited regenerating action during which time a thin skin is caused to form on the drops. The bath is caused to flow without turbulence and eddy currents and serves to move the pellets out of the dropping zone.